The major goal of this proposal during the previous funding cycle was to understand the role of a TNF family member, TRANCE, and its signaling molecules in regulation of immune responses, specifically with regard to dendritic cell (DC)-T cell interaction. This application is a competing renewal to continue our studies initiated to determine how TRANCE regulates DC fates. In the course of these studies, we made a number of intriguing observations that form the basis for the current application. These include: (1) TRANCE promotes DC survival and adjuvanticity via NF-kappaB-dependent Bcl-2 family protein induction, (2) TRANCE is a bona fide modulator of T cell immune responses and tolerance, and (3) TRAF6 is a major signaling molecule in the TRANCE pathway, and plays pivotal roles in the regulation of DC fates by other factors, such as those stimulating CD40 or toll-like receptor signaling pathways. However, it is clear that DC interactions with various factors and with T cells are heterogeneous and complex. Therefore, we will further characterize and define specific signaling events during DC maturation and activation, focusing on TRAF6 since it is a major signaling adapter for TRANCE and other DC-regulatory factors, and study how such signaling events regulate DC-T cell communication by pursuing the following specific aims in the revised application: (1) Determine how TRAF6 regulates DCs by defining functional domains of TRAF6 for DC maturation and activation, (2) Determine potential mechanisms of TRAF6-dependent regulation of DCs by extending our studies of signal transduction pathways via TRAF6 to both DC maturation and activation, and (3) Determine the role of TRAF6-dependent signals in DC-T cell interaction by studying the consequences of immune responses initiated by DCs with genetic defects in the TRAF6 signaling axis. The knowledge gained from this application will provide important insights into the mechanisms of how DC maturation, survival, and activation are regulated by diverse stimulatory factors and their signal transducers, and how T cells and DCs communicate to regulate each other's functions. These will, in turn, provide the basis for design of new immunotherapeutic strategies against tumors, viral diseases or autoimmune diseases that may arise from inadequate or inappropriate immune responses.